Oscillation generation



Patented Jan. 6, 1931 UNITED STATES PATENT o Ficr.

CLARENCE W. HANSELL, OF ROCKY POINT, NEW..YORK, ASSIGNOB TO RADIO CORPORA- TION OF AMERICA, A CORPORATION 01 DELAWARE OSGILLATION GENERATION Application filed March 23, 1928. Serial No. 264,101.

This invention relates to oscillation generation, and more particularly to a method and means for generating oscillations and for controlling the frequency of the gener- 5 ated oscillations.

With a view to reducing fading, narrowing the necessary frequency spectrum of each communication channel, constantly transmitting maximum energy, and for multiplexing, it has been suggested to frequency modulate a constant amplitude carrier, rather than to amplitude modulate a constant frequency carrier.

The usual type of oscillation generator has its frequency determined by the natural resonant frequency of a single tuned circuit, but this is disadvantageous when it is desired to frequency modulate, owing to the structural difiiculty of. providing a resonant circuit the tuning of which may be bothrapidly and linearly varied in response to a control current.

It is an object of my invention to provide for the generation offoscillations and for the control of the frequency of the generated oscillations without varying the natural frequency of a source of oscillations, or more particularly, without varying the resonant frequency of a tuned circuit. This I do by forcing two sources of energy having differing natural frequencies to oscillate at a co1nmon frequency, and varying the relative intensity of the energy supplied by each-of the sources in order to vary the common frequency. The natural frequencies are selected to lie at or beyond the extremes of the desired frequency range.

To provide for the rapid frequency variation needed for transmitting frequency wobbled energy or frequency modulated energy is a more particular objectof my invention, and to this end I employ two electron emission tubes each having regener atively coupled control electrode and anode circuits which are coupled together to oscillate at a common frequency and I tune one of the circuits of each of said tubes to a different extreme frequencyv of the desired range. I then apply the wobble control current or the modulation current through an input transformer, the secondary'of which is coupled in series with the control electrodes of the tubes, to the latter in phase opposition in order to oppositely change their bias. This varies the relative oscillation intensity in each of the oscillation generators, and consequently causes their common frequency, a compromise frequency lying be-- tween the two natural frequencies, to shift in the direction of the frequency of the tube having the lower negative bias at that instant.

One of the advantages of using frequency modulation is the possibility of reducing the necessary frequenc band for each transmitter, but when using a small frequency variation in a high frequency carrier the percentage variation may become so small as to present modulating and demodulating difficulties at the transmitter and receiver. Also, with small frequency variations for the signal it becomes especially important to keep the mean frequency constant. This entire problem may be considered from a different aspect, for it is conceded that the mean frewill the mean frequency oft-he transmitted energy depend thereon, or vary therewith,-

and it is therefore desirable to use a low intermediate frequency. At the same time, in

order to obtain the desired percentage variation in the frequency ofthe high frequency carrier it is necessary to provide a relatively large percentage frequency variation in the energy of intermediate frequency. For this the generator disclosed herein is particularly suitable. I i

The invention is described more in detail 7 in the following specification, which is accompanied by a drawing in which Figure 1 is a wiring diagram for a preferred form of my invention; and

frequencyrange. The cathodes of the tubes 2 and 4 are connected together and to ground, and the control electrodes are connected in series or phase opposition by the secondary of an input transformer 10, which may be by-passed for radio frequencies by condensers 14, and the neutral point of which is connected to a C battery and thence to ground to complete the control electrode to cathode circuits. The anodes of the tubes 2 and 4 are connected together and to one terminal of a feed back coil 16, the other terminal of which is connected to a suitable source of direct anode otential by way of a lead 18. The feed bac coil 16 couples the anode circuits of each of the tubes with its control electrode circuit, formin two oscillation generators, but these osci lation generators are coupled to one another and thereby are forced to oscillate at a common freuency.

With the control electrodes at like bias potentials the common frequency is approximately the mean of the natural frequencies of the circuits 6 and 8, but when the tubes are unequally biased their oscillation intensities are relatively varied, so that the output of one of the tubes predominates over that of the other, and their common frequency shifts accordingly. This variation of bias potential is caused by coupling the wobble control or modulating energy to the primary of the input transformer 10. The modulating energy may be provided, as exemplified in Figure 1, by a speech microphone 30 in series with a battery 32. In this arrangement the two oscillation generators swing cophasially, with respect to the radio frequency, and accordingly the output is taken from both the anodes in parallel, as indicated by the output coil 40. The frequency modulated energy may be fed from the output coil 40 through a power amplifier, and then used directly for transmission. However, to insure constant mean frequency, especially in the case of short wave communication, I prefer to employ a high frequency oscillator especially designed for the production of energy of constant frequency, and to modulate this energy with frequency modulated energy of intermediate frequency, which may be produced as previously described. Thus, referring to Figure 1, there is a high frequency oscillator 42, provided with a cr stal drive 44, the output from which is fe through radio frequency condensers 46 to the carrier suppression modulator tubes 48 in parallel. The intermediate frequency energy is supplied from the coil 40 to the coil 50, which is coupled to the modulator tubes 48 in series. The output coil 52 is connected to the tube anodes in series, in consequence of which the carrier frequency components in each of the tubes are opposed in the halves of the coils 52, and are neutralized. Of the side bands the filter 54 selects one, and this is amplified in a power amplifier 56. To insure constant energy output a limiter may' be used, and preferably the power amplifier is itself made to act as a limiter, by increasing the amplitude of the excitation on each stage beyond the point where an increase in excitation causes appreciable increase in output. This incidentally is the adjustment which is desirable to secure high energy eiiiciency in an amplifier which is to be operated at constant output or with keyed modulation.

The output from the amplifier 56 is radiated from any suitable antenna circuit 58.

The arrangement shown in Figure 2 is quite similar to that shown in Figure 1 except that the oscillation generators are arranged to swing oppositely in phase, with re- 1 spect to the radio frequency, as well as with respect to the wobble frequency. As in Figure 1, there are two electron emission tubes 2 and 4, the control electrode circuits of which include resonant circuits 6 and 8, tuned to extreme frequencies of the desired frequency range, and connected to the cathodes through an input transformer 10 and a C batterylead 12. The anodes, instead of being connected in parallel, are arranged in series by connections to opposite terminals of a coil 116, which is coupled to the-control electrode circuits 6 and 8. The inductances of the latter circuits may be mutually coupled directly to one another, as well as through the coil 116, if desired. The transformer 10 is by-passed for radio frequencies by the radio frequency condensers 14. The direct anode potential is supplied, in this case, through both halves of the coil 116, the

lead 18 being coupled to the center of the coil. The generated output may be transferred to a utilization circuit 142, comprising, in this case, for purpose of illustration, simply a power amplifier 144, and a radiating circuit 146. As before mentioned, the amplifier 144 may be operated as a limiter. Also, obviously, a high frequency source and a side band modulator may be employed, as indicated in Figure 1.

In this modification I have indicated cod communication in which the signalling is ob tained by keying wobble control energy hav- Ill ing constant -amplitude and frequency.

This wobble control alternating current is fed from a generator 60, and its output is controlled b signalling means here exemplified simply y a key 62. The signalled con-' trol energ is fed to the primary of the input trans ormer 10. A plurality of sepa-' rately keyed alternators of different frequencies ma be used for multiplexing, as is more fully isclosed in my copending appl cation Serial Number 212,192, filed August 11, 1927.

I find that the arrangement here disclosed gives a linear response .of frequency change with respect to modulating current amplitude, provided that, the frequency range is.

kept within about ten percent of the-average frequency, which allowable variation is much greater than that found possible b any other method known to me, and su cie'nt so that the radio frequency may be kept quite low, and consequently the mean transmitted frequency may be kept quite constant. For 10% variation the resonant circuits preferably are tuned to frequencies about 15% of the mean frequency apart.

There is no appreciable lag in response, and

v very'little, if any, amplitude variation.

I claim: Y

1. The method of controlling the frequency of generated oscillations which includes forclng two sources of energy having difiering natural fre'quenciesto oscillate at a common frequency, and varying the relative intensity of the energy supplied by each of the sources in order to vary the common frequency.

2. The method ofcontrolling the frequency of oscillations generated in electron emission tube generators which includes generating oscillations in two electron emission tube oscillation generators adjusted to or beyond the extreme frequencies of the desired frequency range, forcing the oscillation generators to oscillate at a common frequency, and changing the relative intensity of the oscillations in each generator in order to control their common frequency.

3. The method of controlling the frequency of oscillations generated in electron emission-tube generators which includes simultaneously generating oscillations in two electron emission tube oscillation generators adjusted to or beyond the extreme frequencies of the desired frequency range, forcing the oscillation generators to oscillate at a common frequency, and changing the relative bias of the control electrodes of tubes to vary the intensity of the oscillations in each generator in order to control their common frequency.

4. The method of wobbling the frequency of oscillations generated in electron emission tube generators which includes generating oscillations in two electron emission tube oscillation g enerators adjusted to or beyond the-extreme frequencies of the desired range offrequency wobble, forcing the oscillation generators to oscillate at a common frequency;and oppositely wobblin the bias of the control electrodes of thetu s to oppositely Wobble the relative oscillation inten sity, in order to wobble the common fre quency.

5. The method of modulating the .frequency of oscillations generated in electron emission tube generators in accordance w th modulating energy which includes "generating oscillations in two electron emissiontube oscillation generators adjustedto or beyond the extreme frequencies of the desired frcquency range, forcing the oscillation generators to oscillate at a common frequency, and applying the modulating energy to the control electrodes of the tubes in phase op-- position to oppositely vary their biasand consequently their oscillation intensity in order to similarly vary the common frequency.

6. The method of transmitting by frequency modulation in accordance with modulating energy which includes generating intermediate frequency oscillations in two electron emission tube oscillation generators tuned to or beyond the extreme frequencies of the desired intermediate frequency range, forcing the oscillation generators ,to oscillate ata common frequency, applying the of the tubes in phase opposition to oppositely vary their bias and consequently their modulating energy to the control electrodes oscillation intensity in order to similarly vary the common frequency, modulating energy of constant high frequency with the frequency modulated intermediate frequen- H supplied from each of said sources in order to vary the common frequency.

8. An arrangement for controlling oscillation frequency over a desired range'comprising two electron emisslon tube oscillation generators adjusted to or beyond the extreme frequencies of the desired range, means coupling the oscillation generators together to force them to oscillate at a common frequency, and means for changing the relative intensity of the oscillations in each generator.

in order tocontrol their common frequency.

9. An arrangement 'for controlling oscillation frequency over a desired range comprising two electron emission tube oscillation generators adjusted to or beyond the extreme frequencies of the desired range, means coupling the oscillation generators together to orce themto oscillate at a common frequency, and means for oppositely changing the bias of the control electrodes of the tubes to vary the intensit of the oscillations in each generator in or er to control their comcontrol electrodes of the-tu s to oppositelyvary the oscillation intensity in order to wobble the common frequency. I

11. An arrangement for generating oscillations and frequency modu ating the generated oscillations in accordance with modulat in" energy comprising two electron emission tube oscillation generators adjusted to or beyond the extreme frequencies of the desired frequency range, means coupling the oscillation generators together to cause them to oscillate at a common frequency, and means coupling the modulating ener to the control electrodes of the tubes in p ase oglposition in order to oppositely vary their ms and consequently the oscillation intensity in order to similarly vary the common frequency.

12. An arrangement for oscillation generation and frequency modulation generator comprising two electron emission tubes each having regeneratively coupled control electrode and anode circuits coupled together to oscillate at acommon frequency, means for tuning one of the circuits of each of said tubes to a different extreme frequency of the desired frequency range, a modulation input circuit coupled to the control electrodes of the tubes in phase opposition, and an output circuit.

13. An arrangement for oscillation generation and frequency modulation comprising two electron emission tubes, a resonant circuit arranged between the control electrode and the cathode of each of said tubes and tuned to the extreme frequencies of the desired frequency range, feed back means in the anode to cathode circuits of said tubes for coupling the resonant circuits to themselves and to one another, a modulation input circuit coupled to the control electrodes of the tubes in phase opposition, and an output circuitr 14. An arrangement for oscillation generation and frequency modulation comprising two electron emission tubes, a resonant circuit arranged between the control electrode and the cathode of each of said tubes and tuned to the extreme frequencies of the desired frequency ra e, a feed back coil coupled to both of sai resonant circuits and connected to the tube anodes and to a source of direct anode potential, a modulation input transformer havin a secondary coupled to the control electrodes of the tubes in phase opposition, and an output circuit coupled to the anode circuit of the tubes.

15. An arrangement for oscillation generation and frequency modulation comprising two electron emission tubes, a resonant circuit arranged between the controlelectrodc and the cathode of each of said tubes and tuned to the extreme frequencies of the desired frequency range, a feed back coil coupled to both of said resonant circuits and connected at one terminal to both of the tube anodes, and at its other terminal to a source of direct anode potential, a modulation input transformer having a secondary coupled to the control electrodes of the tubes in phase opposition, and an output circuit coupled at one end to both of the tube anodes to be fed cophasially.

16. A frequency modulation transmitter comprising two intermediate frequency electron emission tube oscillation generators tuned to extreme intermediate frequencies, means coupling the generators together to force them to oscillate at a common frequency, modulator means for changing the relative intensity of the oscillations in each generator in order to control the common frequency, a source of constant high frequency energy, a modulator for modulating the high frequency ener with the frequency modulated intermediate frequency energy, and means to radiate a portion of the output of the last mentioned modulator.

17. A frequency modulation transmitter comprising two electron emission tubes each having regeneratively coupled control electrode and anode circuits coupled together to oscillate at a common frequency, means for tuning one of the circuits of each of said tubes to adifferent extreme intermediate frequency, a modulation input circuit coupled to the control electrodes of the tubes in phase opposition, a source of constant high frequency energy, a modulator for modulating the high frequency energy with the frequency modulated energy of intermediate frequency,

an am lifier therefor, and means to radiate a portion of the side bands resulting from the last mentioned modulation.

. CLARENCE lV. HANSELL. 

